Weird math problem..... ?

Question

I was doing homework on my calculator and i typed this in:

7.5x7.5 it came up with 56.25 thats not right

then i did this 7x7=49+0.5x0.5 and it came up with this 49.25 now thats right

??????????

why wasnt the first answer right

Answer 1

first answer is right.  You forgot one small step - you need to multiply the 7s by .5, giving you another 3.5 x 2 = 7.  Add that to 49.25 and you get 56.25.

Answer 2

the first answer is correct

Answer 3

Umm... the first answer was right

Answer 4

7.5 * 7.5  is (7 + 0.5) squared.

In algebra (a + b)^2 -- where "a" and "b" are numbers or algebraic terms -- is equal to a^2 + 2*a*b + b^2.

So 7.5 * 7.5

= (7 + 0.5)^2

= 7^2 + 2*7*(0.5) + (0.5)^2

= 49 + 7 + 0.25

= 56.25

The first answer you got is correct.