Prove that the exponential function ex is strictly increasing

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 Multiple Choice QuestionsMultiple Choice Questions

131.

The slope of the normal to the curve y = 2 x2 + 3 sin x at x = 0 is

  • 3

  • 1 third
  • -3

  • -3

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132.

The line y = x + 1 is a tangent to the curve y 2 = 4x at the point

  • (1, 2)

  • (2, 3)

  • (1, -2)

  • (1, -2)

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133. The normal at the point (1, 1) on the curve 2y + x2 = 3 is
  • x + y = 0
  • x – y = 0
  • x + y + 1 = 0
  • x + y + 1 = 0
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134. The normal to the curve x2 = 4 y passing (1, 2) is
  • x + y = 3 
  • x – y = 3
  • x + y = 1
  • x + y = 1
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 Multiple Choice QuestionsShort Answer Type

135. Show that the function f (x) = 2 x + 3 is a strictly increasing function on R.
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136. Without using the derivative show that the function f (a) = 7x – 3 is a strictly increasing function on R.
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137. Show that the function f (x) = x2 is an increasing function in (0, ∞).
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138.

Show that the function f(x) = x2 is a decreasing function in (– ∞  0).

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139.

Construct an example of a functions which is strictly increasing but whose derivative vanishes at a point in the domain of definition of the function.

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140.

Prove that the exponential function ex is strictly increasing on R.


Let f (x) = ex ∴ Df = R
We are to prove that function f (x) = ex is strictly increasing. Here interval is not given. So we will prove that function ex is strictly increasing in its domain.
Now f ' (x) = ex
Three cases arise:
Case I.
                 straight x greater than 0
Syntax error from line 1 column 415 to line 1 column 518. Unexpected '<mlongdiv '.

Case II.
x = 0
∴ f ' (x) = e
x = I > 0
Case III.
               straight x less than 0
therefore space space space straight f apostrophe left parenthesis straight x right parenthesis space equals space straight e to the power of straight x space equals space 1 over straight e to the power of negative straight x end exponent space equals fraction numerator 1 over denominator straight a space positive space quantitiy space end fraction greater than 0
therefore space space space space space in space all space the space three space cases comma space we space have comma space space space straight f apostrophe left parenthesis straight x right parenthesis space equals space straight e to the power of straight x greater than 0
therefore space space space straight f left parenthesis straight x right parenthesis space equals space straight e to the power of straight x space is space straight a space strictly space increasing space function.

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