Solve the system of equations using addition.
4x –y = –6
5x + y = –21

what is the solution of the system?

a. (3,6)
b. (6,3)
c. (–6,–3)
d. (–3,–6)

4x - y = -6 (1)

5x + y = -21 (2)

(1) + (2)

9x = -27

x = -3

from (1)

4 * -3 - y = -6

we solve

y = -6

so the answer is

D ( - 3 , - 6 )

answer: the angel abc is 30°,and the abc is a triangle where the angel bac is 90°

so ac is the half of 24=12ft,and from the pythagorean theorem we find ba

ba=√bc^2-ac^2=√576-144=√432=12√3ft

so bac is 12+12√3=12(1+√3)ft