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The roots of quadratic equation are -5 and 3. Which of the following quadratic equations has these roots

A. X²-8x+15=0
B. X²+8x+15=0
C. X²-2x-15=0
D. X²+2x-15=0


Sagot :

[tex]A.\\\\ x^2-8x+15=0 \\\\x^2-3x-5x+15=0 \\\\x(x-3)-5(x-3)=0\\\\(x-3)(x-5)=0\\\\x-3=0 \ \ or \ \ x+5=0\\ \\x=3\ \ or \ \ x=-5 \\is \ invalid[/tex]

[tex]B.\\\\ x^2+8x+15=0 \\\\x^2+3x+5x+15=0 \\\\x(x+3)+5(x+3)=0\\\\(x+3)(x+5)=0\\\\x+3=0 \ \ or \ \ x+5=0\\ \\x=-3\ \ or \ \ x=-5 \\is \ invalid[/tex]

[tex]C. \\\\x^2-2x-15=0 \\\\x^2-2x-3x+3x -15=0\\\\x^2-5x+3x-15=0 \\\\x(x-5)+3(x-5)=0 \\\\(x-5)(x+3)=0 \\\\x-5=0 \ \ or \ \ x+3=0 \\\\x=5\ \ or \ \ x=-3 \\is \ invalid[/tex]

[tex]D.\\\\ x^2+2x-15=0 \\\\x^2+2x+3x-3x -15=0\\\\x^2+5x-3x-15=0 \\\\x(x+5)-3(x+5)=0 \\\\(x+5)(x-3)=0 \\\\x+5=0 \ \ or \ \ x-3=0 \\\\x=-5\ \ or \ \ x= 3 \\ is \ good \\ \\ Answer : \ D[/tex]