Question

expand (2a-7b -2c)²
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Answer 1

Answer:

formula (a+b+c)^2=a^2+b^2+c^2+2a*b+2b*c+2c*a

so

(2a-7b-2c) ^2

=(2a) ^2+(-7b)^2+(-2c)^2+2*(2a) *(-7b)+2(-7b)*(-2c)+

2(-2c)*(2a)

=4a^2+49b^2+4c^2-28ab+28bc-8ac (ans)..

Answer 2

(a + b+ c) ^2= (a+(b+c)) ^2

a^2+ (b+c) ^2 +2a(b+c)

a^2 +b^2+ c^2 +2bc +2ab + 2ac

a^2 +b^2 + c^2 + 2( ab+ bc + cb)

Know (2a- 5b- 7c) ^2 = (2a) ^2 +(-5b) ^2 +(-7c) ^2 +2(2a) (-5b) + (-5b) (-7c) + (2a) (-7c)

4a^2+ 25b^2+ 49c^2 + 2(35bc - 10ab - 14ac)