Question

stiind ca cos c =3/4 si cos b =1/8 sa se arate ca masura unghiului b= 2× masura unghiului c​

Answer 1

Răspuns:

Explicație pas cu pas:

cos2x= 2cos²x-1

1/8= 2*(9/16)-1=18/16-1=2/16=1/8

deci (1/8) si (3/4) verifica relatia

Answer 2

$\it b=2c \Leftrightarrow cosb=cos2c \Leftrightarrow cosb=2cos^2c-1 \Leftrightarrow \dfrac{1}{8}=2\cdot\Big(\dfrac{3}{4}\Big)^2-1 \Leftrightarrow \\ \\ \\ \Leftrightarrow \dfrac{1}{8}=2\cdot\dfrac{9}{16}-1 \Leftrightarrow \dfrac{1}{8}=\dfrac{9}{8}-1 \Leftrightarrow \dfrac{1}{8}=1\dfrac{1}{8}-1 \Leftrightarrow \dfrac{1}{8}=\dfrac{1}{8}\ (A)$