Question

Answer 1

a) Xét ΔABC vuông tại A ta có:

\(cosC=\dfrac{AC}{BC}\)

\(\Rightarrow cos30^o=\dfrac{10}{BC}\)

\(\Rightarrow BC=\dfrac{10}{cos30^o}\approx11,5\left(cm\right)\)

Theo Py-ta-go ta có:

\(AB=\sqrt{BC^2-AC^2}=\sqrt{\left(11,5\right)^2-10^2}\approx5,7\left(cm\right)\)

\(\Rightarrow\widehat{B}=180^o-90^o-30^o=60^o\)

b) Xét ΔABC vuông tại A ta có:

\(sinB=\dfrac{AC}{BC}\)

\(\Rightarrow sin35^o=\dfrac{AC}{20}\)

\(\Rightarrow AC=sin35^o\cdot20\approx11,5\left(cm\right)\)

Theo Py-ta-go ta có:
\(AB=\sqrt{BC^2-AC^2}=\sqrt{20^2-11,5^2}\approx16,5\left(cm\right)\)

\(\Rightarrow\widehat{C}=180^o-90^o-35^o=55^o\)