Question

Answer 1

Theo đề ta có:

\(cot\alpha=\dfrac{5}{12}\)

Mà: \(cot\alpha=\dfrac{AB}{AC}\)

\(\Rightarrow\dfrac{AB}{AC}=\dfrac{5}{12}\) hay \(\dfrac{30}{AC}=\dfrac{5}{12}\)

\(\Rightarrow AC=\dfrac{30\cdot12}{5}=72\left(cm\right)\) 

Xét tam giác ABC vuông tại A ta có:

\(BC^2=AC^2+AB^2\)

\(\Rightarrow BC=\sqrt{AC^2+AB^2}=\sqrt{30^2+72^2}=78\left(cm\right)\) 

Answer 2

cot a=5/12

=>cot B=5/12

=>AB/AC=5/12

=>30/AC=5/12

=>AC=30*12/5=72(cm)

ΔABC vuông tại A

=>BC^2=AB^2+AC^2

=>\(BC=\sqrt{30^2+72^2}=78\left(cm\right)\)