Question

Calculati 7a+3b-4c, daca a+b=70 si a-c=40

Answer 1

Răspuns:

370

Explicație pas cu pas:

a + b = 70

a - c = 40

Exprimam necunoscutele prin a:

a + b = 70 <=> b = 70 - a

a - c = 40 <=> c = a - 40

Calculam:

7a + 3b - 4c = 7a + 3(70 - a) - 4(a - 40) = 7a + 210 - 3a -4a + 160 = 370

Answer 2

a+b=70 - relatia 1

a-c=40 - relatia 2

(aduni cele 2 relatii)

2a+b-c=110

+relatia 1

3a+2b-c=180

+relatia 1

4a+3b-c=250

+relatia 2

5a+3b-2c=290

+relatia 2

6a+3b-3c=330

+relatia 2

7a+3b-4c=370