√21CosA-? ,если sinA=0.4

Question

√21CosA-? ,если sinA=0.4

Answer 1

Cosa=√(1-sin²a)=√(1-0.4²)=√(1-0.16)=√0.84=0.2*√21
√21cosa=√21*0.2*√21=0.2*21=4.2