Find the coefficient of x^2 in the expansion of (2x-1)^7

1 answer:

7 0

(2x-1)^7
=(2x)^7+7(2x)^6(-1)+21(2x)^5(-1)^2+35(2x)^4(-1)^3+35(2x)^3(-1)^4+21(2x)(-1)^5+7(2x)(-1)^6+(-1)^7
=128x^7+7(64x^6)(-1)+21(32x^5)+35(16x^4)(-1)+35(8x^3)+21(4x^2)(-1)+14x-1
=128x^7-7(64x^6)+672x^5-35(16x^4)+280x^3-21(4x^2)+14x-1
=128x^7-448x^6+672x^5-560x^4+280x^3-84x^2+14x-1
The coefficient of x^2 is -84

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A number has the property that its square is equal to 84 more than five times the number. Enter all numbers that have this prope

Liono4ka [1.6K]

Answer:

The numbers for which the given property hold true are 12 and -7

Step-by-step explanation:

Let the number be $x$ .

As per the given statement:

Square of the number ( $x^{2}$ ) is 84 more than five times of the number ( $5x+84$ ).

Writing in the equation form:

$x^{2} =5x+84$

To find:

All the numbers for which above equation holds true.

Solution:

$x^{2} =5x+84$

Let us solve the above equation by rearranging the terms and then let us find the roots of the equation.

It is a quadratic equation(i.e. maximum power of $x$ is 2) so it will have 2 solutions i.e. 2 values of $x$ for which the above equation will hold true.

$x^{2} -5x-84=0$