NCERT Solutions for Class 12 Maths Chapter 11 Three Dimensional Geometry Ex 11.1 are part of NCERT Solutions for Class 12 Maths. Here we have given NCERT Solutions for Class 12 Maths Chapter 11 Three Dimensional Geometry Ex 11.1.

Board |
CBSE |

Textbook |
NCERT |

Class |
Class 12 |

Subject |
Maths |

Chapter |
Chapter 11 |

Chapter Name |
Three Dimensional Geometry |

Exercise |
Ex 11.1 |

Number of Questions Solved |
5 |

Category |
NCERT Solutions |

## NCERT Solutions for Class 12 Maths Chapter 11 Three Dimensional Geometry Ex 11.1

**Question 1.**

If a line makes angles 90°, 135°, 45° with the and z axes respectively, find its direction cosines.

**Solution:**

Direction angles are 90°, 135°, 45°

Direction cosines are

**Question 2.**

Find the direction cosines of a line which makes equal angles with coordinate axes.

**Solution:**

Let direction angle be α each

∴ Direction cosines are cos α, cos α, cos α

But l² + m² + n² = 1

∴cos² a + cos² a + cos² a = 1

**Question 3.**

If a line has the direction ratios – 18,12, -4 then what are its direction cosines?

**Solution:**

Now given direction ratios of a line are -8,12,-4

∴ a = -18,b = 12,c = -4

Direction cosines are

**Question 4.**

Show that the points (2,3,4) (-1,-2,1), (5,8,7) are collinear.

**Solution:**

Let the points be A(2,3,4), B (-1, -2,1), C (5,8,7).

Let direction ratios of AB be

**Question 5.**

Find the direction cosines of the sides of the triangle whose vertices are (3,5, -4), (-1,1,2) and (-5,-5,-2).

**Solution:**

The vertices of triangle ABC are A (3, 5, -4), B (-1,1,2), C (-5, -5, -2)

(i) Direction ratios of AB are (-4,-4,6)

Direction cosines are

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