GCSE Maths | Quadratics

Factorising quadratics
$$x^2+7x+12 = (x+3)(x+4)$$

Question 1

Factorise the following quadratics.

(a) $x^2+7x+12$

(b) $x^2+6x+8$

(c) $x^2+5x+6$

(d) $x^2+8x+7$

(e) $x^2+4x+4$

(f) $x^2+8x+15$

(g) $x^2+6x+9$

(h) $x^2+11x+28$

Show Answers

(a) $(x+3)(x+4)$

(b) $(x+2)(x+4)$

(c) $(x+2)(x+3)$

(d) $(x+1)(x+7)$

(e) $(x+2)^2$

(f) $(x+3)(x+5)$

(g) $(x+3)^2$

(h) $(x+4)(x+7)$

Question 2

Factorise the following quadratics.

(a) $x^2+x-12$

(b) $x^2+5x-6$

(c) $x^2+3x-10$

(d) $x^2+3x-4$

(e) $x^2+2x-48$

(f) $x^2+4x-32$

(g) $x^2+2x-35$

(h) $x^2+8x-33$

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(a) $(x-3)(x+4)$

(b) $(x-1)(x+6)$

(c) $(x-2)(x+5)$

(d) $(x-1)(x+4)$

(e) $(x-6)(x+8)$

(f) $(x-4)(x+8)$

(g) $(x-5)(x+7)$

(h) $(x-3)(x+11)$

Question 3

Factorise the following quadratics.

(a) $x^2-3x-10$

(b) $x^2-x-20$

(c) $x^2-6x-27$

(d) $x^2-2x-3$

(e) $x^2-x-12$

(f) $x^2-4x-12$

(g) $x^2-4x-21$

(h) $x^2-6x-55$

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(a) $(x-5)(x+2)$

(b) $(x-5)(x+4)$

(c) $(x-9)(x+3)$

(d) $(x-3)(x+1)$

(e) $(x-4)(x+3)$

(f) $(x-6)(x+2)$

(g) $(x-7)(x+3)$

(h) $(x-11)(x+5)$

Question 4

Factorise the following quadratics.

(a) $x^2-6x+9$

(b) $x^2-9x+20$

(c) $x^2-9x+14$

(d) $x^2-13x+22$

(e) $x^2-9x+8$

(f) $x^2-12x+32$

(g) $x^2-15x+36$

(h) $x^2-14x+48$

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(a) $(x-3)^2$

(b) $(x-4)(x-5)$

(c) $(x-2)(x-7)$

(d) $(x-2)(x-11)$

(e) $(x-1)(x-8)$

(f) $(x-4)(x-8)$

(g) $(x-3)(x-12)$

(h) $(x-6)(x-8)$

Question 5

Factorise the following quadratics.

(a) $x^2-9x+8$

(b) $x^2+24x+23$

(c) $x^2-5x-14$

(d) $x^2-7x+12$

(e) $x^2+12x+36$

(f) $x^2-2x-63$

(g) $x^2+14x+24$

(h) $x^2+17x+60$

(i) $x^2-11x+30$

(j) $x^2-4x-32$

(k) $x^2-2x-63$

(l) $x^2-16x-17$

Show Answers

(a) $(x-1)(x-8)$

(b) $(x+1)(x+23)$

(c) $(x-7)(x+2)$

(d) $(x-3)(x-4)$

(e) $(x+6)^2$

(f) $(x-9)(x+7)$

(g) $(x+2)(x+12)$

(h) $(x+5)(x+12)$

(i) $(x-5)(x-6)$

(j) $(x-8)(x+4)$

(k) $(x-9)(x+7)$

(l) $(x-17)(x+1)$

$$a^2-b^2 = (a-b)(a+b)$$
$$x^2-25 = (x-5)(x+5)$$

Question 6

Factorise the following quadratics using the difference of two squares.

(a) $x^2-25$

(b) $y^2-49$

(c) $w^2-100$

(d) $x^2-4$

(e) $c^2-64$

(f) $x^2-1$

(g) $x^2-900$

(h) $y^2-9$

(i) $16-x^2$

(j) $1-y^2$

(k) $81-x^2$

(l) $144-h^2$

(m) $x^2-y^2$

(n) $a^2-c^2$

(o) $9x^2-25$

(p) $4y^2-1$

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(a) $(x-5)(x+5)$

(b) $(y-7)(y+7)$

(c) $(w-10)(w+10)$

(d) $(x-2)(x+2)$

(e) $(c-8)(c+8)$

(f) $(x-1)(x+1)$

(g) $(x-30)(x+30)$

(h) $(y-3)(y+3)$

(i) $(4-x)(4+x)$

(j) $(1-y)(1+y)$

(k) $(9-x)(9+x)$

(l) $(12-h)(12+h)$

(m) $(x-y)(x+y)$

(n) $(a-c)(a+c)$

(o) $(3x-5)(3x+5)$

(p) $(2y-1)(2y+1)$

Solving quadratics by factorising
$$(x-1)(x-3)=0 \implies x=1 \text{ or } x=3$$

Question 7

Solve the following quadratics.

(a) $(x-1)(x-3)=0$

(b) $(y-4)(y-9)=0$

(c) $(m+1)(m+6)=0$

(d) $(x-3)(x+2)=0$

(e) $(t+7)(t-3)=0$

(f) $(k-10)(k+9)=0$

(g) $(w+5)(w+11)=0$

(h) $(y-8)(y-2)=0$

(i) $(x+3)(x-9)=0$

Show Answers

(a) $x=1$ or $x=3$

(b) $y=4$ or $y=9$

(c) $m=-1$ or $m=-6$

(d) $x=3$ or $x=-2$

(e) $t=-7$ or $t=3$

(f) $k=10$ or $k=-9$

(g) $w=-5$ or $w=-11$

(h) $y=8$ or $y=2$

(i) $x=-3$ or $x=9$

Solving quadratics with the quadratic formula
$$x = \frac{-b\pm\sqrt{b^2-4ac}}{2a}$$
$$x^2+5x+1=0$$ $$x = \frac{-5\pm\sqrt{21}}{2}$$

Question 8

Solve the following quadratics using the quadratic formula.

(a) $x^2+5x+1=0$

(b) $2x^2+7x+2=0$

(c) $4x^2+8x+3=0$

(d) $x^2+2x-4=0$

(e) $3x^2+4x-5=0$

(f) $2x^2+5x-10=0$

(g) $x^2-4x+2=0$

(h) $7x^2-6x+1=0$

(i) $3x^2-10x+4=0$

(j) $x^2-x-11=0$

(k) $x^2-6x-20=0$

(l) $2x^2-x-9=0$

Show Answers

(a) $x=\dfrac{-5\pm\sqrt{21}}{2}$

(b) $x=\dfrac{-7\pm\sqrt{33}}{4}$

(c) $x=-\dfrac{1}{2}$ or $x=-\dfrac{3}{2}$

(d) $x=-1\pm\sqrt{5}$

(e) $x=\dfrac{-2\pm\sqrt{19}}{3}$

(f) $x=\dfrac{-5\pm\sqrt{105}}{4}$

(g) $x=2\pm\sqrt{2}$

(h) $x=\dfrac{3\pm\sqrt{2}}{7}$

(i) $x=\dfrac{5\pm\sqrt{13}}{3}$

(j) $x=\dfrac{1\pm3\sqrt{5}}{2}$

(k) $x=3\pm\sqrt{29}$

(l) $x=\dfrac{1\pm\sqrt{73}}{4}$

Completing the square
$$x^2+bx+c = \left(x+\frac{b}{2}\right)^2 - \left(\frac{b}{2}\right)^2 + c$$
$$y = x^2-8x-2$$ $$y = (x-4)^2-18$$ Minimum point: $(4,-18)$

Question 9

Complete the square in the following quadratics, then state the coordinates of the maximum or minimum point.

(a) $y=x^2-8x-2$

(b) $y=x^2+6x+10$

(c) $y=x^2-4x+1$

(d) $y=x^2+4x+9$

(e) $y=x^2+8x+20$

Show Answers

(a) $(x-4)^2-18$; minimum point $(4,-18)$

(b) $(x+3)^2+1$; minimum point $(-3,1)$

(c) $(x-2)^2-3$; minimum point $(2,-3)$

(d) $(x+2)^2+5$; minimum point $(-2,5)$

(e) $(x+4)^2+4$; minimum point $(-4,4)$

$$y = 4x^2-8x+28$$ Factor out the leading coefficient first: $$y = 4\left(x^2-2x\right)+28 = 4(x-1)^2+24$$ Minimum point: $(1,24)$

Question 10

Complete the square in the following quadratics, then state the coordinates of the maximum or minimum point.

(a) $y=4x^2-8x+28$

(b) $y=5x^2+20x+15$

(c) $y=3x^2+24x+45$

(d) $y=4x^2-8x+16$

(e) $y=5x^2+10x$

Show Answers

(a) $4(x-1)^2+24$; minimum point $(1,24)$

(b) $5(x+2)^2-5$; minimum point $(-2,-5)$

(c) $3(x+4)^2-3$; minimum point $(-4,-3)$

(d) $4(x-1)^2+12$; minimum point $(1,12)$

(e) $5(x+1)^2-5$; minimum point $(-1,-5)$

Factorising harder quadratics
$$2x^2+7x+5 = (x+1)(2x+5)$$

Question 11

Factorise the following quadratics.

(a) $2x^2+7x+5$

(b) $2x^2+11x+15$

(c) $2x^2+9x+10$

(d) $3x^2+13x+4$

(e) $3x^2+4x+1$

(f) $3x^2+8x+4$

(g) $5x^2+13x+6$

(h) $5x^2+26x+5$

(i) $7x^2+10x+3$

(j) $11x^2+47x+12$

(k) $2x^2+17x+36$

(l) $5x^2+62x+24$

Show Answers

(a) $(x+1)(2x+5)$

(b) $(x+3)(2x+5)$

(c) $(x+2)(2x+5)$

(d) $(x+4)(3x+1)$

(e) $(x+1)(3x+1)$

(f) $(x+2)(3x+2)$

(g) $(x+2)(5x+3)$

(h) $(x+5)(5x+1)$

(i) $(x+1)(7x+3)$

(j) $(x+4)(11x+3)$

(k) $(x+4)(2x+9)$

(l) $(x+12)(5x+2)$

Solving quadratic inequalities
$$(x-4)(x-1)<0$$ The critical values are $x=1$ and $x=4$. Since the graph is a positive $u$-shape, it's below zero between the roots: $$1<x<4$$

Question 12

Solve the following quadratic inequalities.

(a) $(x-4)(x-1)<0$

(b) $(x-2)(x+1)<0$

(c) $(x+7)(x+3)\leq 0$

(d) $(x-5)(x+4)\leq 0$

(e) $x(x-9)>0$

(f) $(x+6)(x-5)>0$

(g) $(x+10)(x+1)\geq 0$

(h) $(x-7)(x+7)\geq 0$

(i) $(x+8)(x+2)<0$

(j) $(x-4)(x+7)\geq 0$

(k) $(x+1)(x-5)\leq 0$

(l) $(x-12)(x-11)>0$

Show Answers

(a) $1<x<4$

(b) $-1<x<2$

(c) $-7\leq x\leq -3$

(d) $-4\leq x\leq 5$

(e) $x<0$ or $x>9$

(f) $x<-6$ or $x>5$

(g) $x\leq -10$ or $x\geq -1$

(h) $x\leq -7$ or $x\geq 7$

(i) $-8<x<-2$

(j) $x\leq -7$ or $x\geq 4$

(k) $-1\leq x\leq 5$

(l) $x<11$ or $x>12$


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