Please tell me the solution and the steps required to get solution to this.
Let sin(a)= 1/ sqrt(5) 0 < a < 90 degrees
cos(b)= 3/ sqrt(10) 0< b <90
then what is sin(a+b) equal to?
$\displaystyle \sin(a+b) = \sin(a)\cos(b)+\sin(b)\cos(a)$
And
$\displaystyle \sin(a)= \frac{1}{ \sqrt{5}}$
$\displaystyle \cos(b)= \frac{3}{ \sqrt{10}}$
To sub into the above formula.
Use $\displaystyle \sin^2a+\cos^2a = \sin^2b+\cos^2b =1$
To find $\displaystyle \sin(b)$ and $\displaystyle \cos(a)$
I had forgotten to clarify that I must do this all without a calculator, making the suggestion by anonymous kinda mood. I must thanks pickles thought because now I can solve any problem that is similar, I suppose then there are similar identities for say sin(a-b) and the sort, right?