Math; Complete the square for the expressions
posted by asdf on .
I have a number of problems I'm having problem with but they start with the example given in the book
2x^2  10x
=2(x^2  5x)
=2{[x(5/2)]^2  [(5/2)^2]}
=2[x(5/2)]^2  (25/2)
Why isn't (5/2)^2 (25/4)?
I'm struggling with the exercises as well.
3x^2  24x
I get 3(x4)^2  16 or if I try to follow the example, 3(x4)^2  32, but the answer at the back of the book is 3(x4)^2  48

I meant, "Why isn't (25/2)^2 (25/4)?"

You seem to have forgotten a basic rule of multiplying fractions.
a/b * c/d = ac/(bd)
The square of any fraction a/b is a^2/b^2.
For example, 2/3 of 2/3 = (2/3)^2 = 4/9
and (25/2)^2 = 625/4
Looking at your second problem,
3x^2  24x
= 3(x^2 8x) Now add and subtract 48
= 3(x^2 8x +16) 48
= 3(x4)^2 48