Question

(3a+2.5b)^2=9a^2+6.25b^2+*
Please help before Thursday

Answer 1

Given that, ( 3a + 2.5b )² = 9a² + 6.25b² + *

We know that, ( x + y )² = x² + y² + 2xy

According to the above problem, we get

( 3a + 2.5b )² = (3a)² + (2.5b)² + (2×3a×2.5b)

( 3a + 2.5b )² = 9a² + 6.25b² + 15ab

Therefore,

The sign " * " should be 15ab.

• 15ab is the right answer.

Answer 2

Explanation:

We have (x + y)² = (x + y)(x + y) = x² + 2xy + y².

Let x be 3a and y be 2.5b.

Therefore (3a + 2.5b)²

= (3a)² + 2(3a)(2.5b) + (2.5b)²

= 9a² + 15ab + 6.25b².

Hence the '*' sign should be replaced with 15ab.