Solving quadratic equations | Harder example | Math | SAT | Khan Academy

Watch Sal work through a harder Solving quadratic equations problem.

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[MindMathMoney]

Important to know this one in and out! Great breakdown!

[unazaasif]

Just do back solving and find solution in 30 sec instead of this long formula solution.

[aanya-tlpl]

lmfao im studying for the psat 8/9 and my brain is very close to exploding

[muhammadhanzlaqadri]

It would have been simple if you just inserted the values in options for x then it wouldn't take to do the whole procedure as equality would've been sufficient.

[anandsaroop]

One other method is that, Put the two values of each option and see which option satisfies the equation

[rajeshsoundararajan]

I didn't understand why you would split 84 into 4x21. How should I know when to do this? Is there a rule?

[uhunomaotasowie]

Completing d square method is way faster

[dexivoje]

This is way too slow. You take advantage of the property of the solutions in that they multiply to c (in this case -20) and add to -b (in this case -2). SO choice D jumps up immediately. This holds when equation is in the form ax2+bx+c.