An algebra problem by Mohammad Oladzad

Algebra Level 3

If y = 2 x 2 2 x + 2 y=2x^2-2x+2 , then what is the minimum of this function?


The answer is 1.5.

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2 solutions

Atul Shivam
Nov 9, 2015

Here we can use a bit calculus Given y = 2 x 2 2 x + 2 y=2x^2-2x+2 ,in order to get minimum value of y y we have to show that d 2 y d x 2 > 0 \frac{d^2y}{d x^2}>0

Now let us see :-

d y d x = 4 x 2 \frac{dy}{dx}=4x-2 and d 2 y d x 2 = 4 > 0 \frac{d^2y}{d x^2}=4 >0 so y y will be minimum when d y d x = 4 x 2 = 0 \frac{dy}{dx}=4x-2=0 ie, x = 1 2 x=\frac{1}{2} put x = 1 2 x=\frac{1}{2} in the above equation than y = 2 × 1 2 2 2 × 1 2 + 2 y=2×\frac{1}{2^2}-2×\frac{1}{2}+2 which is 1.50 \boxed{1.50}

Kay Xspre
Oct 5, 2015

2 x 2 2 x + 2 = 2 ( x 2 x + 1 ) = 2 ( x 2 2 ( 1 2 ) x + ( 1 2 ) 2 + 3 4 ) = 2 ( x + 1 2 ) 2 + 3 2 2x^2-2x+2 = 2(x^2-x+1) = 2(x^2-2(\frac{1}{2})x+(\frac{1}{2})^2+\frac{3}{4}) = 2(x+\frac{1}{2})^2+\frac{3}{2}

Provided that for all real number n n , n 0 n \geq 0 , then 2 ( x + 1 2 ) 2 0 2(x+\frac{1}{2})^2 \geq 0 2 ( x + 1 2 ) 2 + 3 2 3 2 2(x+\frac{1}{2})^2+\frac{3}{2} \geq \frac{3}{2} 2 x 2 2 x + 2 3 2 2x^2-2x+2 \geq \frac{3}{2}

Site shows this as solution to problem "x^log5+5^logx=250 find logx". Something messed up on the site.

Kuntal Shah - 5 years, 8 months ago

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Yeah you are right, previously I was also confused about it.

Atul Shivam - 5 years, 7 months ago

I think problem is a bit o v e r r a t e d overrated

Atul Shivam - 5 years, 7 months ago

Why did the question changed?

Alaudin Noor - 5 years, 7 months ago

your solution is beautiful but there is an easier way...

mohammad oladzad - 5 years, 8 months ago

so, this is a solution?

Alaudin Noor - 5 years, 7 months ago

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