If A is a 3 × 3 invertible matrix, then what will be the value

Subject

Mathematics

Class

CBSE Class 12

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 Multiple Choice QuestionsShort Answer Type

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1.

If A is a 3 × 3 invertible matrix, then what will be the value of k if det(A–1) = (det A)k.


straight A to the power of negative 1 end exponent space equals space fraction numerator Adj space straight A over denominator vertical line straight A vertical line end fraction
therefore space vertical line straight A to the power of negative 1 end exponent vertical line space equals space fraction numerator vertical line Adj space straight A vertical line over denominator vertical line straight A vertical line end fraction
equals space fraction numerator vertical line straight A vertical line to the power of 3 minus 1 end exponent over denominator vertical line straight A vertical line end fraction
left square bracket because space If space straight A space is space straight a space non space singular space matrix space of space order space straight n comma space then space vertical line adj space left parenthesis straight A right parenthesis space equals space vertical line straight A vertical line to the power of straight n minus 1 end exponent right square bracket

equals space fraction numerator vertical line straight A vertical line squared over denominator vertical line straight A vertical line end fraction
As space we space are space given space that space vertical line straight A to the power of negative 1 end exponent vertical line space equals space vertical line straight A vertical line to the power of straight k
therefore space straight k space equals negative 1
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2.

Determine the value of the constant ‘k’ so that the function  is continuous at x = 0.

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3.

If a line makes angles 90° and 60° respectively with the positive directions of x and y axes, find the angle which it makes with the positive direction of the z-axis.

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4.

Show that all the diagonal elements of a skew symmetric matrix are zero.

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5.
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6.

The volume of a sphere is increasing at the rate of 3 cubic centimetres per second. Find the rate of increase of its surface area, when the radius is 2 cm.

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7.

Show that the function f(x) = 4x3 – 18x2 + 27x – 7 is always increasing on R.

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8.

Prove that 

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9.

Using properties of determinants, prove that 

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10.

Let find a matrix D such that CD – AB = O.

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