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1.

Find the magnitude, in radians and degrees, of the interior angle of aregular(i)pentagon                (ii)octagon(iii)     heptagon               (iv) duodecagon.

Answer» Sum of the interior angles of n-sided polygon is given as `(n-2)*pi`.
`:.` Interior angle of regular polygon `= ((n-2)*pi)/n`
(i) Interior angle of regular pentagon `= ((5-2)*pi)/5 = (3pi)/5` radians
Interior angle in degrees `= 3/5*180 = 108^@`
(ii) Interior angle of regular octagon`= ((8-2)*pi)/8 = (6pi)/8 = (3pi)/4` radians
Interior angle in degrees `= 3/4*180 = 135^@`
(iii) Interior angle of regular heptagon `= ((7-2)*pi)/7 = (5pi)/7` radians
Interior angle in degrees `= 5/7*180 = (900/7) ^@`
(iv) Interior angle of regular duodecagon`= ((12-2)*pi)/12 = (5pi)/6` radians
Interior angle in degrees `= 5/6*180 = 150 ^@`
2.

In a right-angled triangle, the difference between the two acute angles is `(pi/15)^(c )`. Find the angle in degrees.

Answer» Clearly, the sum of the two acute anles of a right triangleis `90^(@)`.
Difference between the acute angles `= (pi/15)^(c )= (pi/15 xx 180/pi)^(@) = 12^(@)`.
Let the two acute be `x^(@)` and `y^(@)` . Then,
`x + y= 90 "…….."(i)`
`x- y = 12 "............" (ii)`
Solving (i) and (ii), we get `x = 51` and `y = 39`.
Hence, the angles of triangleare `51^(@), 39^(@)` and `90^(@)`.
3.

Find the angle between the minute hand and the hour hand of a clock at 7.20 am

Answer» Angle traced by the hour hand in `12` hours `= 360^(@)`,
Angle traced by it in `7 h 20` min i.e., in `22/3` ho `= (360/12 xx 22/3)^(@) = 220^(@)`
Angle traced by the minute hand in `60` min `= 360^(@)`.
Angle traced by the minute hand in `20` min `(360/12 xx 20)^(@) = 120^(@)`.
Hence, the required anle between the two hands.
`= (220^(@) - 120^(@)) = 100^(@)`.
4.

A wheel makes 360 revolutions in one minute.Through how many radians does it turn in one second?

Answer» Number of revolutions made in 60 secons `= 360`.
Number of revolutions made in `1` second = `(360)/(60) = 6`.
Angle moved in 1 revolutions made in 1 second` = (360)/(60) = 6`.
Angle moved in 1 revolution `= (2pi)^(c )`
Angle moved in 6 revolutions `= (2pi xx 6)^(c) = (12pi)^(c )`.
5.

The large hand of a clock is 42 cm long. How many centimetres does its extremity move in 20 minutes.

Answer» Correct Answer - `88 cm`
6.

The angles of a quadrilateral are in AP, and the greatest angle is double the least. Express the least angle in radians.

Answer» Correct Answer - `((pi)/3)^(c )`
7.

Find in degrees the angle through which a pendulum swings if its lengthis `50c m`and the tip describes an arc of length `10c m`.

Answer» Here, length of arc, `l = 10cm`
Length of pendulam, `r = 50cm`
We know, `rtheta = l`
`=>50theta = 10`
`=>theta = 1/5 radian`
`=>theta = 1/5(360/(2pi))^@ = (36/pi)^@`