Question

plz solve 6th and 7th one​

Answer 1

Answer:

6)

1+ (27/125)a^3 + 9a/5 + (27/25)a^2,

=1^3+(3a/5)^3 + 3* (1^2)*(3a/5) + 3*(1)*(3a/5)^2,

= (1+3a/5)^3

7)

(2x-5y)^3-(2x+5y)^3,

=(2x-5y-2x-5y)[(2x-5y)^2+(2x-5y)(2x+5y)+(2x+5y)^2],

= (-10y) [(4x^2+25y^2-20xy)+(4x^2-25y^2)+(4x^2+25y^2+20xy)],

= (-10y) [ 12x^2+25y^2],

=-120x^2y-250y^3.

used formulae :

• (a+b)^3 = a^3+ b^3+ 3a^2b+ 3ab^2,
• a^3-b^3 = (a-b)(a^2+ab+b^2).

hope it helps u...