Question

5a-11b+21c=?
2a+b-3c=15
a-4b+8c=25

Answer 1

2a + b - 3c = 15 (1)

[a - 4b + 8c = 25 ] ×3 (2)

2a +b -3c =15 (3)

3a -12b +24c = 75 (4)

se aduna

_____________________

2a +3a +b -12b -3c +24c =15+75

5a -11b +21c = 90 exact ce s-a cerut prin enunt!!!!