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# Linear and quadratic systems — Basic example

Watch Sal work through a basic Linear and quadratic systems problem.

## Want to join the conversation?

• my ti84 only shows (16,5) co-ordinate :/
• Yeah not every problem will allow a calculator. My reliance on a calculator came back to bite me, too.
• plugging in the answers is probably the best and fastest method to do this math
• oh this question is SNEAKY! trying to trick me and preventing me from getting more POINTS!
• I think substitution works better with this problem + it is easier!
• i can't understand this method
is there any else
• Or simple, use the elimination method
• Substitution is more efficient in this case as x is already isolated.
• can anyone who explain me why is nt A?
• Let's plug in the numbers and see if it works:

2y + 6 = x
y^2 - 9 = x

I'll substitute x = -5 and y = 3 in the system of equations above.

2 * 3 + 6 = -5 --> 12 =/= -5
9 - 9 = -5 --> 0 =/= -5

Neither equations work with the (-5, 3) pair, so A is definitely not the answer.
(1 vote)
• I understood the ending clearly and easily but the starting is too complicated
• wouldn't it be y=-5 and y=3
(1 vote)
• If you have y-5=0, and you plug in -5, it'll be -10, not 0. You add 5 to both sides, which means y=5

y+3=0 is the same thing. Subtract each side by 3 and you'll get y=-3.