1.

Prove that `(2+sqrt(x))^(4)+(2-sqrt(x))^(4)= 2(16+24x+x^(2))`.

Answer» ` ( a + b ) ^ ( 4 ) + ( a - b ) ^ ( 4) = [.^ ( 4 ) C_(0) a^ ( 4 ) + .^ ( 4) C_(1) a^(3)b +.^(4)C_(2)a^(2)b ^ ( 2) + .^(4) C_(3)ab^(3) + .^(4)C_(4)b^(4)]`
`+ [.^(4)C_(0) a^(4) + .^ (4)C_(1) a^(3) b + .^(4) C_(2)a^(2)b^(2) - .^(4)C_(3)ab^(3) + .^(4) C _(4)b^(4)]`
`=2[.^(4) C _ (0) a^(4) + .^(4) C _(2) a^(2) b^(2) + .^(4) C _(4) b^(4) ]= 2 [a^(4) + 6a^(2) b^(2) + b^(4)].`
Putting `a=2 and b= sqrt(x),` we get
`(2+ sqrt(x) )^(4) + ( 2 - sqrt(x))^(4) = 2[2^(4) + 6 xx 2 ^(2) xx ( sqrt(x))^(2) + ( sqrt(x))^(4) ] = 2 ( 16+ 24x + x^(2)).`


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