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High school mathematics trigonometric function! Urgent! thank you
Solution: 1.c? =a? +b? -3√ 10ab/5

CosC=3√ 10/ 10 According to the cosine theorem, then when a, C∈(0, π), sinc = √10, Sina = √ 5/5.

cos2C=2cos? C- 1=4/5

cosB=cos(π-A-C)=-cos(A+C)

=sinAsinC-cosAcosC

=-√2/2

When B∈(0, π), B=3π/4.

2. Sina: sinc = a: c = √ 5/5: √10/√ 2:1.

A-c=√2- 1, so a=√2, c= 1.

S△ABC=? sinBac=? ×√2/2 ×√2× 1= 1/2