For me, I usually use factorization or quadratic formula.
Factorization example:
x(x−5)=−4x2−5x+4=0(x−1)(x−4)=0Set each factor to 0.x−1=0x=1x−4=0x=4∴x=1 and x=4
Quadratic formula example:
x2−x−1=0x=−(−1)±√(−1)2−(4)(1)(−1)2(1)=1±√52∴x=1+√52 and x=1−√52
Just for you to know: The solution of ax2+bx+c=0 is x=−b±√b2−4ac2a
Complementation of the square example: (I usually call it completing the square)
x2+8x+15=0x2+8x+16−1=0(x+4)2=1x+4=±√1=±1x=−3 and x=−5
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