1.

Please solve question no. 19,21(i),(ii) and (iii) ASAPBut if you don't know it's answer then don't answer this question so that someone who know it's answer can answer it​

Answer»

Answer:

21(ii) Tn = sin^n x+ cos ^nx

T4= sin^4x + cos^4x

T6 = sin^6x + cos^6x

2T_6 -3T_4+10

= 2(sin^6x+cos ^6)-3(sin^4x+ cos ^4x)+10

= 2{(sin^2x)^3+(cos ^2x)^3}- 3{(sin^2x)^2+(cos^2x)^2}+10

[a^3+b^3=(a+b)(a^2-ab+b^2)

a^2+b^2 = (a+b)^2-2ab & sin^2 THETA + cos^2 theta= 1]

USING these

= 2[(sin^2x+cos^2x)(sin^4x+cos^4x-sin^2x cos^2x)3sin^4x- 3cos^4x+10

= 2sin^4x+2cos^4x-2sin^2x cos^2x - 3sin^4x - 3cos^4x+10

= - sin^4x - cos^4x -2sin^2x cos^2x+10

= 10-[(sin^2x)^2+(cos^2x)^2+2sin^2x cos ^2x]

=10-(sin^2x+cos^2x)^2

=10 - 1 =9


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