已知sinacosa=2/5且√cos=-cosa.则sina+cosa

已知sinacosa=2/5且√cos=-cosa.则sina+cosa
已知sinacosa=2/5且√cos=-cosa.则sina+cosa

已知sinacosa=2/5且√cos=-cosa.则sina+cosa
sina^2+cosa^2=1
∴（sina+cosa）^2=sina^2+cosa^2+2sinacosa=1+(2/5)*2=9/5
又√cos>0
∴-cosa>0,从而cosa0,则-1

先求（sina+cosa）²，由于（sina+cosa）²=sina²+cosa²+2sinacosa=1+2×2/5=9/5，因为sina×cosa=2/5>0.所以sina>0,cosa>0.也就是(sina+cosa)>0,所以sina+cosa=9/5的开平方，取正值

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Birth Date: August 4,ugg Australia, 1961 Birthplace: Honolulu, Hawaii, United States Religion: Christianity Nationality: American Spouse: Michelle Robinson Residence: Chicago, Illinois University Attended Harvard Law SchoolColumbia University B.A.)Occidental College Occupation: Author Political party: Democratic Party Office: President of the United States Website: Barack Obama Products from Amazon.com No related products. Subscribe to this page
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