Bmat 2012 q 8 simpley

[Michael_cohen]

8. E

G = 5 + √7 (9 – R)² + 9

G – 5 = √7 (9 – R)² + 9

Squaring both sides,

(G – 5)² = 7 (9 – R)² + 9

(G – 5)² – 9 = 7 (9 – R)²

(G – 5)² – 9 = (9 – R)²
7

Square Rooting on both sides,

√(G – 5)² – 9 = 9 – R
7

{√(G – 5)² – 9} – 9 = – R
7

To change the sign of R from negative to positive, we need to multiply both sides by -1

(-1) x {√(G – 5)² – 9} – 9 = – R (-1)
7

R = 9 – {√(G – 5)² – 9}
7

i saw thats the way to solve it but i cant understand why its cant be D

[Juliette]

Hi
You have to isolate the square on one side before finding the root
And you have to isolate the root before finding the square value
I think it’s because that way you keep the equation in its most simplified form
That might be where your error is