sedinalana

Verified answer

4(cos20-sin20)/(√2sin25)=4(cos20-cos70)/(√2sin25)
=-8*sin45*sin(-25)/(√2sin25)=4√2sin25/(√2sin25)=4
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sin20=sin(90-70)=cos70
cosa-cosb=-2sin[(a+b)/2*sin(a-b)/2]