For Rihan
Question 8
Given:
First term
Last term
Sum
(a) Formula to calculate sum of first terms
S_n = \frac{n}{2}(a + l)
(b) Find the total number of terms
220 = \frac{n}{2}(4 + 40)
220 = \frac{n}{2} \times 44
220 = 22n
n = 10
✅ Answer: Number of terms = 10
(c) What should be added to the third term so that first three terms form a GP?
AP terms:
1st = 4
2nd = 8
3rd = 12
Let required number =
New third term =
For GP:
(8)^2 = 4(12 + x)
64 = 48 + 4x
4x = 16
x = 4
✅ Answer: 4
Question 11
Given:
Length is 8 m more than breadth
Area = 384 sq.m
Let breadth = m
Length =
(a) Form the equation
x(x + 8) = 384
x^2 + 8x - 384 = 0
(b) Find length and breadth
(x + 24)(x - 16) = 0
x = 16
Breadth = 16 m
Length = 24 m
✅ Answer: Length = 24 m, Breadth = 16 m
(c) How much should length be decreased to make it a square?
24 - 16 = 8 \text{ m}
✅ Answer: 8 m
Question 12
Given:
A circle with centre O
∠RMP and ∠RNP are angles standing on the same arc RP
∠ROP is the central angle
(a) Relation between ∠RMP and ∠RNP
Angles standing on the same arc are equal.
\angle RMP = \angle RNP
✅ Answer: Equal
(b) Find ∠MRN
Given:
\angle MRN = (7x - 2)^\circ
\angle MPN = (3x + 10)^\circ
Since they stand on the same arc:
7x - 2 = 3x + 10
4x = 12
x = 3
\angle MRN = 7(3) - 2 = 19^\circ
✅ Answer: 19°
(c) Relation between central and inscribed angle
Central angle is twice the inscribed angle.
\angle ROP = 2\angle RMP
✅ Verified
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