bonjour
( 2 x + 1 )² - 4 = ( 2 x + 1 - 2 ) ( 2 x + 1 + 2 )
= ( 2 x- 1 ) ( 2 x + 3 )
4 x² - 5 x + 7 = - 14
on remplace par - 3
4 ( - 3 )² - 5 ( - 3 ) + 7 = - 14
4 *9 + 15 + 7 = - 14
36 + 22 = - 14
58 ≠ - 14
donc faux
cos BC = AB/BC
cos BC = 25/BC
BC = cos 15 * 25 = ≈ 24 m
- 5 * - 4 + 2*- 4 - 14
= 20 - 8 - 14
= - 2
