Bonjour,
1) On applique le théorème de Thalès.
AS/AB = ST/BC
42/125 = ST/75
ST = 42 * 75 / 125
ST = 25,2 m
2) (3x + 5)(x - 4)
= 3x² - 12x + 5x - 20
= 3x² - 7x - 20
3) Un multiple de 7.
4) 3(x + 1) + (x + 1)(x - 5)
= (x + 1)(3 + x - 5)
= (x + 1)(x - 2)
5) F(x) = x² - 4x
F(10) = 10² - 4(10)
f(10) = 100 - 40
f(10) = 60
