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plz show solve using substitution.

-3x + y = 15 and
-8x − 7y = -18

x = -122/13 OR 9.3846

Step-by-step explanation:

First, take a look at the second equation. Add 8x to the other side.

-7y= 8x -18

Then, divide by -7 to get a regular "y=" equation.

y= 8/7x -18/7

Move on the the first equation. Let's get "y" by itself. Add 3x to the other side.

y= 3x +15

Considering both equations are equal to Y, set them equal ( except the "y" part )

8/7x - 18/7 = 3x + 15

Multiply all by seven so that there are no fractions.

8x - 18 = 21x + 105

Subtract 8x from both sides.

-17 = 13x + 105

Subtract 105 from both sides.

-122 = 13x

Divide by 13 on both sides.

x = 9.3846

Or if you don't want decimals, just say x = -122/13

Quick Note: I made a mistake. I had looked at the second equation at -18. The answer is incorrect but the method of solving is correct. Also, make sure to plug in the value of x to get Y.

step-by-step explanation: a reaction is first order. if the initial reactant concentration is 0.0200 m, and 25.0 days later the concentration is 6.25 x 10-4 m, then its half-life is:

arithmetic sequence

step-by-step explanation:

given that a sequence has terms as

19, 15, 11,

this is represented on a graph

the pattern indicates that the sequence is an arithmetic sequence with i term

a=19 and common difference d =-4

any general term

thus the sequence is reduced by 4 for each successive term starting from 1 and nth term is

24-5n.

first negative term would start after 5th term

5th term =24-25< 0

from 5th term onwards the sequence would be negative.