I'm solving systems and I don't understand how to do it pls helpp

Use the process of elimination. I'll only do one example since you have 4.

Step-by-step explanation:

Let's do the first question.

2x-3y=-11

2x+y=9

Our goal here is to be left with one variable to solve, this way we can use the answer for that variable to find the other. A.K.A only find X to plug into the equation to find Y. To do this, we'll use the process of elimination, in which we need to cancel out a variable.

X seems the easiest here. To cancel 2 (in the top equation), you need to have a -2. And that -2 needs to be the x coefficient in the 2nd equation, in order for us to "cancel" it out. To get -2, you multiply 2 by -1.

-1(2x+y)= -1(9)

Note that whatever you do to one side, you need to do it to both sides! Hence, why I also multiplied 9 by -1. You should now be left with:

-2x -y = -9

Now, we cancel out the positive 2 and -2 from both equations by adding the two equations.

2x-3y= 11

+

-2x-y=-9

X cancels out, so we're left with -4y=-20. Solve for Y, which is 5.

-4y=-20

y=5

Now that you have the Y value, plug it into any of the two equations to find your X value.

2x-3y=11

2x-3(5)=11

2x-15=11

2x=26

x=13

And voilah! Our Y value is 5, and our X value is 13.

It's pretty simple once you understand what's going on. All that we did was to cancel out one variable (either X or Y) in the two equations so that we're left with only one variable to solve. If we cancel out X, we only need to solve for Y. You do this by manipulating one of the two equations (doesn't matter which one). Once you find either X or Y, all you need to is to plug it into one of the original equations. Then, you'll have both X and Y.

And that my friend, is the process of elimination. Good luck!

pls ask

according to the triangle sum theorem, all the angles in a triangle must add up to 180 degrees. if we know one angle is already 90, we do 180-90=90. the other 2 angles must add up to 90, exactly.

step-by-step explanation: