N
ngoc1thu2


1. giải pt:
$(sin^3(x/2)+1/(sin^3(x/2))^2+(cos^3(x/2)+1/cos^3(x/2))^2=81/4.(cos4x)^2$
$(sin^3(x/2)+1/(sin^3(x/2))^2+(cos^3(x/2)+1/cos^3(x/2))^2=81/4.(cos4x)^2$
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