Sinb = SIN (a+c) = sinA cosC+cosAS INC = √ 5 COSC, given cosA, we can find sinA, bring SINA and COSA into this equation respectively, and leave s Inc and COSC in the equation, we can find tanC, and the first question is over.

The second question-

The tanC obtained above should be √5.

I think it should be calculated as follows:

(sinc) 2 = (sinc) 2/[(sinc) 2+(cosc)2], and the denominator of the molecule is divided by (cosc) 2 at the same time to obtain:

(sinC) 2 = (tanc) 2/[(tanc) 2+1], after finding the square of sinC, the square root must be positive, so we can find sinc, get this, and the rest will be easy, that's all.