Explore IDNLearn.com's extensive Q&A database and find the answers you're looking for. Get timely and accurate answers to your questions from our dedicated community of experts who are here to help you.

Find the roots of the equation by completing the square: 3x^2-6x-2=0. Prove your answer by solving by the quadratic formula.

Sagot :

Calculating delta: 
Δ=b²-4ac
a=3
b=-6
c=-2
Δ=36-4*3*(-2)=36+24=60
√Δ=√60
Delta is positive so there are two roots:
x1=[tex] \frac{ -b+ \sqrt[2]{delta} }{2a} [/tex]
x1=[tex] \frac{6+ \sqrt{delta} }{2*3} [/tex]=[tex] \frac{3+ \sqrt{15} }{3} [/tex]
x2=[tex] \frac{3- \sqrt{15} }{3} [/tex]
[tex]3x^2-6x-2=0\\\\(\sqrt3\ x)^2-2\cdot\sqrt3\ x\cdot\sqrt3+(\sqrt3)^2-(\sqrt3)^2-2=0\\\\(\sqrt3\ x-\sqrt3)^2-3-2=0\\\\(\sqrt3\ x-\sqrt3)^2=5\iff\sqrt3\ x-\sqrt3=-\sqrt5\ \vee\ \sqrt3\ x-\sqrt3=\sqrt5\\\\\sqrt3\ x=\sqrt3-\sqrt5\ \vee\ \sqrt3\ x=\sqrt3+\sqrt5\ \ \ \ \ |multiply\ both\ sides\ by\ \sqrt3\\\\3x=3-\sqrt{15}\ \vee\ 3x=3+\sqrt{15}\ \ \ \ \ \ \ |divide\ both\ sides\ by\ 3\\\\x=\frac{3-\sqrt{15}}{3}\ \vee\ x=\frac{3+\sqrt{15}}{3}[/tex]



[tex]Prove:\\\\3x^2-6x-2=0\\a=3;\ b=-6;\ c=-2\\\Delta=b^2-4ac\to\Delta=(-6)^2-4\cdot3\cdot(-2)=36+24=60\\\\x_1=\frac{-b-\sqrt\Delta}{2a};\ x_2=\frac{-b+\sqrt\Delta}{2a}\\\\\sqrt\Delta=\sqrt{60}=\sqrt{4\cdot15}=\sqrt4\cdot\sqrt{15}=2\sqrt{15}\\\\x_1=\frac{6-2\sqrt{15}}{2\cdot3}=\frac{3-\sqrt{15}}{3}\ \vee\ x_2=\frac{6+2\sqrt{15}}{2\cdot3}=\frac{3+\sqrt{15}}{3}[/tex]
Your presence in our community is highly appreciated. Keep sharing your insights and solutions. Together, we can build a rich and valuable knowledge resource for everyone. Thank you for choosing IDNLearn.com for your queries. We’re here to provide accurate answers, so visit us again soon.