JEE mathematics

Sponsor Area

Question
CBSEENMA11015565

AB is a vertical pole with B at the ground level and A at the top. A man finds that the angle of elevation of the point A from a certain point C on the ground is 60°. He moves away from the pole along the line BC to a point D such that CD = 7 m. From D the angle of elevation of the point A is 45°.
Then the height of the pole is

  • fraction numerator 7 square root of 3 over denominator 2 end fraction. fraction numerator 1 over denominator square root of 3 begin display style minus end style begin display style 1 end style end fraction straight m
  • fraction numerator 7 square root of 3 over denominator 2 end fraction. left parenthesis square root of 3 plus 1 right parenthesis space straight m
  • fraction numerator 7 square root of 3 over denominator 2 end fraction. left parenthesis square root of 3 minus 1 right parenthesis space straight m
  • fraction numerator 7 square root of 3 over denominator 2 end fraction. fraction numerator 1 over denominator square root of 3 begin display style plus end style begin display style 1 end style end fraction

Solution

B.

fraction numerator 7 square root of 3 over denominator 2 end fraction. left parenthesis square root of 3 plus 1 right parenthesis space straight m


BD = AB = 7 + x
Also AB = x tan 60° = x√3
∴ x√3 = 7+x
straight x space equals space fraction numerator 7 over denominator square root of 3 minus 1 end fraction

AB space equals space fraction numerator 7 square root of 3 over denominator 2 end fraction left parenthesis square root of 3 plus 1 right parenthesis

Sponsor Area

Question
CBSEENMA11015566

A die is thrown. Let A be the event that the number obtained is greater than 3. Let B be the event that the number obtained is less than 5. Then P (A ∪ B) is 

  • 3/5

  • 0

  • 1

  • 2/5

Solution

C.

1

A = {4, 5, 6} , B = {1, 2, 3, 4} .
Obviously P (A ∪ B) = 1.

Question
CBSEENMA11015567

A focus of an ellipse is at the origin. The directrix is the line x = 4 and the eccentricity is 1/2. Then the length of the semi−major axis is 

  • 8/3

  • 2/3

  • 5/3

  • 4/3

Solution

A.

8/3

Major axis is along x-axis.
straight a over straight e minus space ae space equals space 4
straight a space open parentheses 2 minus 1 half close parentheses space equals 4
straight a space equals 8 over 3

Question
CBSEENMA11015568

A parabola has the origin as its focus and the line x = 2 as the directrix. Then the vertex of the parabola is at 

  • (0, 2)

  • (1, 0)

  • (0,1)

  • (2,0)

Solution

B.

(1, 0)

vertex (0,1) 

Question
CBSEENMA11015569

The point diametrically opposite to the point P (1, 0) on the circle x2+ y2 + 2x + 4y − 3 = 0 is 

  • (-3,4)

  • (-4,3)

  • (-3,-4)

  • (3,4)

Solution

C.

(-3,-4)

Centre (− 1, − 2)
Let (α, β) is the required point
fraction numerator straight alpha plus 1 over denominator 2 end fraction space equals space minus space 1 space and space fraction numerator straight beta plus 0 over denominator 2 end fraction space equals space minus space 2