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1 mark

The slopes of two lines are 1 and
3


. What is the angle between these two lines?

  1. A
    15
  2. B
    30
  3. C
    45
  4. D
    60

Solution & Step-by-step Explanation

Let the slopes of the two lines be m
1

=1 and m
2

=
3


.
The acute angle θ between two lines is given by the formula:

tanθ=



1+m
1

m
2


m
2

−m
1







Substituting the given values:

tanθ=



1+1×
3



3


−1




=
3


+1
3


−1


To simplify, multiply the numerator and denominator by (
3


−1):

tanθ=
(
3


)
2
−1
2

(
3


−1)
2


=
3−1
3+1−2
3




=
2
4−2
3




=2−
3



We know that:

tan(15

)=2−
3



Therefore, θ=15

.

Practice this question

Try it yourself before checking the explanation above.

The slopes of two lines are 1 and
3


. What is the angle between these two lines?
A
15
B
30
C
45
D
60

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