Question

If a = 30°, b = 60° and c = 135°, then what is the value of sin3a + cos3b + tan3c – 3sin a cos b tan c?

Answer 1

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

It’s quite easy actually to find this, if you know basic algebraic expansion. Since (a-b)^3 = (a-b)(a-b)(a-b), you expand one pair first, and then the last a-b.

That being said, it’s useful to memorise basic algebraic identities. This is a list of a few easy ones:

Answer 2

Answer:

0

Step-by-step explanation:

a=30 then sin30 = 1/2

b=60 then cos 60 =1/2

c=135 i.e. (90+4 5) , tan (90+45)= -cot 45= -1

now Sin^3a= (1/2)^3= 1/8

cos^3b = (1/2)^3 = 1/8

tan^3c = (-1)^3=-1

so

1/8)(+(1/8)-1-3*(1/2)*(1/2)*(-1)

=0