a) 2x(4x-1)=10
Expand
8x^2-2x=10
Divide all terms by 2
4x^2-x=5
4x^2-x-5=0
4x^2+4x-5x-5=0
4x(x+1)-5(x+1)=0
(4x-5)(x+1)=0
x is equal to -1 and 5/4
but, in this case, the side of a rectangle cannot be negative, so the only answer that is mathematically possible is 5/4
b) substitute 5/4 into given expressions
length: 4(5/4)-1 which is 4cm
width: 2*5/4 which is 2.5cm
c) plus all four sides together
2.5+2.5+4+4 which is 13cm
