Please help me!

r^2 + s^2 = 1     square both sides

r^4 + 2(rs)^2 + s^4 = 1

r^4 + s^4 = 1 - 2(rs)^2

(7/8) = 1  - 2(rs)^2   rearrange

2(rs)^2  = 1 - 7/8

2(rs)^2 = 1/8    divide both sides by 2

(rs)^2 = 2/ 16 = 1/8   take the square root of both sides

(rs) = ±√(1/8) = ±√(1/2√2) = ±√2/4

And since r and s are positive real numbers, take the positive root

PLEASE HELP ME! I REALLY NEED HELP!!!!!!!!!!!!!!  o_o

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