By using factorisation, solve $(x - 3)(2x + 8) = -12. Answer: x = ... Solve the equation 42x−3−3x+2=1.\frac{4}{2x-3} - \frac{3}{x+2} = 1. Give your solutions correct to two decimal places. Answer: x = ...

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Worked solution

3(a)

1. Expand the left-hand side and rearrange into quadratic form

(x−3)(2x+8)=−12(x-3)(2x+8)=-12
2x2+8x−6x−24=−122x^2+8x-6x-24=-12
2x2+2x−24=−122x^2+2x-24=-12
2x2+2x−12=02x^2+2x-12=0

2. Simplify the quadratic equation and factorise

2x2+2x−12=02x^2+2x-12=0
Divide by 22:
x2+x−6=0x^2+x-6=0
(x+3)(x−2)=0(x+3)(x-2)=0

3. Use the zero product property to find the values of $x$

(x+3)(x−2)=0(x+3)(x-2)=0
So,
x+3=0orx−2=0x+3=0 \quad \text{or} \quad x-2=0
x=−3orx=2x=-3 \quad \text{or} \quad x=2

Answer

x=−1x=-1 or x=−2x=-2

3(b)

1. State the restrictions and multiply by the common denominator

2x−3≠02x-3 \ne 0 and x+2≠0x+2 \ne 0, so x≠32x \ne \dfrac32 and x≠−2x \ne -2.

Multiply both sides of
42x−3−3x+2=1\frac{4}{2x-3}-\frac{3}{x+2}=1
by (2x−3)(x+2)(2x-3)(x+2):
4(x+2)−3(2x−3)=(2x−3)(x+2).4(x+2)-3(2x-3)=(2x-3)(x+2).

2. Expand and rearrange into quadratic form

4x+8−6x+9=2x2+x−64x+8-6x+9=2x^2+x-6
−2x+17=2x2+x−6-2x+17=2x^2+x-6
2x2+3x−23=02x^2+3x-23=0

3. Solve the quadratic equation and round to two decimal places

Using a=2a=2, b=3b=3, c=−23c=-23,
x=−3±32−4(2)(−23)2(2)x=\frac{-3\pm\sqrt{3^2-4(2)(-23)}}{2(2)}
x=−3±1934x=\frac{-3\pm\sqrt{193}}{4}
x=2.723… or x=−4.223…x=2.723\ldots \text{ or } x=-4.223\ldots
Correct to two decimal places,
x=2.72 or x=−4.22.x=2.72 \text{ or } x=-4.22.

Answer

x=−2.97x=-2.97 or x=1.47x=1.47

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