Find two real numbers b such that the algebraic expression is a perfect square trinomial.
16x^2 + bxy +25y^2

Question

Find two real numbers b such that the algebraic expression is a perfect square trinomial. 
 16x^2 + bxy +25y^2

saifoo.khan · Answer

http://images.flatworldknowledge.com/redden/redden-eq09_034.jpg

anonymous · Answer

@saifoo.khan please explain your answer

saifoo.khan · Answer

Do you know how to do the completing square?

anonymous · Answer

I now believe its 20 and -20.
I tried working it out again :

16x^2 + bxy + 25y^2
$$(16x ^{2} + 20xy) + (20xy +25y ^{2})$$
I got 20xy from doing a*c, 16 * 25. Which equals 40. And then i to the square root of that to get 20.

anonymous · Answer

This then factors down to $$(4x+5y)^{2}$$ which is a perfect square

saifoo.khan · Answer

You're right!

saifoo.khan · Answer

So  b is going to be 40.

anonymous · Answer

Oh yes thats right! Almost overlooked that

hartnn · Answer

you know it can b -40 too, right ?

hartnn · Answer

thts why they asked in the question, "two" values