已知tanα=1/2,求(sinα)^2+3sinα·cosα的值

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已知tanα=1/2,求(sinα)^2+3sinα·cosα的值
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已知tanα=1/2,求(sinα)^2+3sinα·cosα的值
已知tanα=1/2,求(sinα)^2+3sinα·cosα的值

已知tanα=1/2,求(sinα)^2+3sinα·cosα的值
(sinα)^2+3sinα·cosα=[(sinα)^2+3sinα·cosα ]÷1
=[(sinα)^2+3sinα·cosα]÷((sinα)^2 +(cosα)^2) (1的代换)
=[ (tanα)^2 +3tanα] ÷[(tanα)^2 +1] (分子分母同除以(cosα)^2 )
=(0.25+3×0.5]÷[ 0.25+1]
=1.75÷1.25=1.4