Question

Please help, I would appreciate it

Answer 1

Answer:

-5x + 8y = -21

3x - 4y = 15

8y = 5x - 21

y = 5/8x - 21/8

3x - 4y = 15

-4y = -3x + 15

y = 3/4x - 15/4

5/8x - 21/8 = 3/4x - 15/4

-1/8x = -9/8x

x = 9

3x - 4y = 15

3(9) - 4y = 15

27 - 4y = 15

-4y = -12

y = 3

(9, 3)

Answer 2

Answer:

  (9, 3)

Step-by-step explanation:

My favorite way to solve equations like this is using a graphing calculator. For Desmos, one only needs to type the equations into the input column, click on one of them, and highlight the point of intersection to see the coordinates there.

__

The usual ways to solve these are by substitution or elimination. Another way they can be solved is using Cramer's rule, which provides a formula for the solution based on the coefficients.

  ax +by = c

  dx +ey = g

__

  x = (bg -ec)/(bd -ea) . . . . . . note the crossing pattern of the values in the products

  y = (cd -ga)/(bd -ea) . . . . . . the denominator is the same as above

__

Using these formulas, we get ...

  x = (8(15) -(-4)(-21))/(8(3) -(-4)(-5)) = (120 -84)/(24 -20) = 36/4 = 9

  y = (-21(3) -15(-5))/4 = (-63 +75)/4 = 12/4 = 3

The solution is (x, y) = (9, 3).

Doing the same by elimination involves the same amount of math and a lot more writing.