# Ex 5.1, 6 - Chapter 5 Class 7 Lines and Angles

Last updated at Sept. 11, 2018 by Teachoo

Last updated at Sept. 11, 2018 by Teachoo

Transcript

Ex 5.1, 6 (Method 1) In the given figure, ∠1 and ∠2 are supplementary angles. If ∠1 is decreased, what changes should take place in ∠2 so that both the angles still remain supplementary.Given, ∠1 and ∠2 are supplementary angles, We know that, If two angles are supplementary, their sum is 180° So, ∠1 + ∠2 = 180° → ∠1 = 180° − ∠2 Now, If ∠1 is decreased by x, ∠1 becomes (∠1 − x). And ∠2 is changed to ∠3, such that (∠1 − x) and ∠3 are also supplementary angles. Then, (∠1 − x) + ∠3 = 180° 180° − ∠2 − x + ∠3 = 180° ∠3 = 180° − 180° + ∠2 + x ∠3 = ∠2 + x So, if ∠ 1 is decreased by x ∠ 2 should be increased by x Hence, in order to make ∠1 and ∠2 supplementary, ∠2 will have to be increased by the same value as ∠1 was decreased. Ex 5.1, 6 (Method 2) In the given figure, ∠1 and ∠2 are supplementary angles. If ∠1 is decreased, what changes should take place in ∠2 so that both the angles still remain supplementary.Given, ∠1 and ∠2 are supplementary, So, ∠1 + ∠2 = 180° If ∠ 1 is decreased, suppose it is decreased by 10° So, (Angle 1 New) + (Angle 2 New) = 180° (∠1 − 10°) + (Angle 2 New) = 180° Thus, Angle 2 must be increased by 10° Our sum becomes (∠1 − 10°) + (∠2 + 10°) = 180° ∠1 + ∠2 + 10° − 10° = 180° ∠1 + ∠2 = 180° Suppose ∠1 is decreased by 20° So, ∠2 must be increased by 20° Our sum becomes (∠1 − 20°) + (∠2 − 20°) = 180° ∠1 + ∠2 + 20° − 20° = 180° ∠1 + ∠2 = 180° ∴ ∠2 must be increased by the same value as ∠1 is being decreased.

Ex 5.1

Ex 5.1, 1 (i)

Ex 5.1, 1 (ii)

Ex 5.1, 1 (iii)

Ex 5.1, 2 (i)

Ex 5.1, 2 (ii)

Ex 5.1, 2 (iii)

Ex 5.1, 3 (i)

Ex 5.1, 3 (ii)

Ex 5.1, 3 (iii)

Ex 5.1, 3 (iv)

Ex 5.1, 3 (v)

Ex 5.1, 3 (vi)

Ex 5.1, 4 Important

Ex 5.1, 5

Ex 5.1, 6 Important You are here

Ex 5.1, 7

Ex 5.1, 8 Important

Ex 5.1, 9 Important

Ex 5.1, 10

Ex 5.1, 11

Ex 5.1, 12 (i)

Ex 5.1, 12 (ii) Important

Ex 5.1, 13 (i) Important

Ex 5.1, 13 (ii)

Ex 5.1, 13 (iii)

Ex 5.1, 13 (iv)

Ex 5.1, 13 (v)

Ex 5.1, 13 (vi)

Ex 5.1, 14 Important

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Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 10 years. He provides courses for Maths and Science at Teachoo.