Question

Calculati masura unghiului A​

Answer 1

$\Delta ABC \: ,AB=5,BC=7,AC=6$

$cos\widehat{A}=?$

Ne folosim de teorema cosinusului :

${BC}^{2}={AB}^{2}+{AC}^{2}-2\times AB \times AC\times cos\widehat{A}$

${7}^{2} = {5}^{2} + {6}^{2} - 2 \times 5 \times 6 \times cos\widehat{A}$

$49 = 25 + 36 - 60cos\widehat{A}$

$60cos\widehat{A} = 61 - 49$

$60cos\widehat{A} = 12$

$cos\widehat{A} = \frac{12}{60}$

$cos\widehat{A} = \frac{1}{5}$