When x is real number what is the maximum value of 2 x 2 + 3 x + 6 x + 2 ?
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Let y = 2 x 2 + 3 x + 6 x + 2 .
Now,
2 y x 2 + 3 y x + 6 y = x + 2 . ⇒ 2 y x 2 + ( 3 y − 1 ) x + 6 y − 2 = 0
Let this be a quadratic equation in x . We have to know where this equation has real roots. So we will use the discriminant.
( 3 y − 1 ) 2 − 4 ( 2 y ) ( 6 y − 2 ) ≥ 0 .
Solving this inequality, we will get y ∈ [ 1 3 1 , 3 1 ] . So our max is 3 1 .
Nice approach! I like how you turned it into a question about the discriminant of the quadratic equation.
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I too agree with Calvin Lin . Very different approach.
actually this type of method in coaching cintres
f ( x ) = 2 x 2 + 3 x + 6 x + 2 f ′ ( x ) = . . . 2 x 2 + 3 x + 6 − ( x + 2 ) ( 4 x + 3 ) = 0 2 x 2 − 4 x 2 + 3 x − 1 1 x = 0 x = 0 o r x = − 4 x = 0 g i v e M a x . M a x = f ( 0 ) = 1 / 3 1 / 3
Hey how did u give red color in latex please tell me
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In this case, the red color occurred because he had a minor Latex mistake. Specifically, he typed in f^', instead of f'. The ' is already understood to be a superscript, hence the confusion to Latex. I have since fixed this, and his equations appear correctly (eg they were supposed to be fractions).
Otherwise, to add color, you can use \color{red} { x^2 + 2 }, which will give x 2 + 2 .
i did it the same way
find the critical pts. then you got the answer, maxima minima if im right :D.....
then zero is the value of x
common sense and logic are needed heheheh
f(x)=(x+2)/(2x2+3x+6) we study f we find that f(0) is the max value of f(x) and f(0)= 1/3
Find first derivative and equate =0 ; to find values of x, they are 0 and -4. And check the sign of second derivative for values of x. If second derivative is -ve at particular value of x (here it is 0), put this value at place of x to find max. value.
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2 x 2 + 3 ( x + 2 ) x + 2
= 2 ( x 2 − 4 ) + 3 ( x + 2 ) + 8 x + 2
= 2 ( x − 2 ) + 3 + x + 2 8 1
= 2 ( x + 2 ) + x + 2 8 − 5 1
we will consider maxima for positive real values (can you answer why?)
f ( x ) m i n = 2 2 ( x + 2 ) + x + 2 2 3 = 2 4 = 8
Thus maximum = 8 − 5 1 = 3 1