i have this for my math review & i just don't seem to get it ...

what is (.9x+.8y) ^2

Can you take the quantity [ x + y ] and square it?

Can you take the quantity [ x + 2y ] and square it?

Then you should have no trouble with the square of (.9x +.8y).

The square of any binomial (expression with 2 terms) is

(square of the first term)

+ (square of the second term)

+ 2 times (product of the terms).