Câu `4:`

`triangleMNP` vuông tại `M`

`cos P=(MP)/(NP)=9/15=0,6`

`-> hatP ~~ 53^o8'`

Câu `5:`

Ta có `20^2+21^2=29^2=841`

`triangleABC` vuông tại `B`

`sin C=(AB)/(AC)=20/29`

`-> hatC~~44^o`

Câu `6:`

`BC=sqrt(6^2+8^2)=10 \ cm`

`tan B=(AC)/(AB)=8/6=4/3`

`-> hatB~~53^o`

Câu `7:`

`a)`

`AB=sqrt(BC^2-AC^2)=sqrt(5^2-4^2)=3`

`sin B=(AC)/(BC)=4/5=>0,8=>hatB~~53^o8'`

`-> hatC=90^o-hatB~~36^o52'`

`b)`

`hatC=90^o-hatB=90^o-60^o=30^o`

`AB=(AC)/(tanB)=6/(tan 60^o)=2sqrt3`

`BC=(AC)/(sinB)=6/(sin 60^o)=4sqrt3`

`c)`

`BC=sqrt(AB^2+AC^2)=sqrt(5^2+12^2)=13`

`tanB=(AC)/(AB)=12/5=2,4=>hatB~~67^o23'`

`hatC=90^o-hatB~~22^o37'`

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