Toán Lớp 9: cho tanx=-4
tính giá trị bthuc A= sin^2x+sin2x-4cos^2x/sin2x-2cos^2x
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Toán Lớp 9: cho tanx=-4
tính giá trị bthuc A= sin^2x+sin2x-4cos^2x/sin2x-2cos^2x
Comments ( 2 )
=(sin^2x-2sinxcosx-4cos^2x)/(2sinxcosx-2cos^2x)
={(sin^2x)/(cos^2x)-(2sinxcosx)/(cos^2x)-(4cos^2x)/(cos^2x)}/((2sinxcosx)/(cos^2x)-(2cos^2x)/cos^2x)
=(tan^2x-2tanx-4)/(2tanx-2)
$\textit{Thay tanx=-4 vào A, ta được:}$
=((-4)^2*-2*(-4)-4)/(2*(-4)-2)
=(16+8-4)/(-8-2)
=-(20)/10=-2