Kevin is 4 times as old as Daniel and is also 6 years older than Daniel. How old is Kevin?

1 answer:

5 0

There are numerous important information's already given in the question. Based on these information's, the answer can be deduced.
Let us assume the age of Daniel = x years
Let us assume the age of Kevin = y years
Then
y = 4x
and
y = x + 6
So
4x = x + 6
4x - x = 6
3x = 6
x = 6/3
= 2 years
So
Age of Kevin = 4 * 2 years
= 8 years

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Prove that sinA-sin3A+sin5A-sin7A/cosA-cos3A-cos5A+cos7A= cot2A

MAVERICK [17]

Write the left side of the given expression as N/D, where
N = sinA - sin3A + sin5A - sin7A
D = cosA - cos3A - cos5A + cos7A
Therefore we want to show that N/D = cot2A.

We shall use these identities:
sin x - sin y = 2cos((x+y)/2)*sin((x-y)/2)
cos x - cos y = -2sin((x+y)/2)*sin((x-y)2)

N = -(sin7A - sinA) + sin5A - sin3A
= -2cos4A*sin3A + 2cos4A*sinA
= 2cos4A(sinA - sin3A)
= 2cos4A*2cos(2A)sin(-A)
= -4cos4A*cos2A*sinA

D = cos7A + cosA - (cos5A + cos3A)
= 2cos4A*cos3A - 2cos4A*cosA
= 2cos4A(cos3A - cosA)
= 2cos4A*(-2)sin2A*sinA
= -4cos4A*sin2A*sinA

Therefore
N/D = [-4cos4A*cos2A*sinA]/[-4cos4A*sin2A*sinA]
= cos2A/sin2A
= cot2A

This verifies the identity.

4 0

3 years ago

-5/8 - 2/7 (fraction form only)<br> P.S. help me please :)

vesna_86 [32]

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