(5a & 5b)
start from the right side for No.5a,b
6a)
Sn=n/2(2a+(n-1)d)
A=1, d=2, n=n
Sn=n/2(2*1+(n-1)2)
N/2(2+2,-2)
=n/2*2=n^2
6b)
6c)
(7a)
x-2/4 +2/2x
Cross multiply
2x(x-2)=4(x+2)
Opening the bracket
2x^2-4x = 4x+8
Collect like terms together
2x^2-4x-4x-8=0
2x^2-8x-8=0
Solving with completing the square method
2x^2-8x=8
Divide through with the coefficient of x^2
2x^2/2-8x/2=8/2
X^2-4x=4
Half of coefficient of x
(-4 x 1/2)^2 = (-2)^2
X^2-4x+(-2)^2=4+(-2)^2
X^2-4x+(-2)^2=4+4
(x-2)^2=8
X-2:square root 8
X=2 + or - squar root 8
X=2+ square root 8 or x=2- square root 8
X=2+2.828=4.828
X=2-2.828= -0.828
X=4:83 or - 0.83.
(7B)
(8a & 8b)
(9a & 9b)
(13a & 13b)
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