In a geometric sequence, the first term is 3 and the common ratio is 2. What is the sum of the first 9 terms?
1 answer:
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Given :
- ZC = 90°
- CD is the altitude to AB.
A = 65°.
To find :
- the angles in △CBD and △CAD if m∠A = 65°
Solution :
In Right angle △ABC,
we have,
=> ACB = 90°
=> CAB = 65°.
So,
=> ACB +
CAB+
ZCBA = 180° (By angle sum Property.)
=> 90° + 65° + CBA = 180°
=> 155° +CBA = 180°
=> CBA = 180° - 155°
=> CBA = 25°.
In △CDB,
=> CD is the altitude to AB.
So,
=> CDB = 90°
=> CBD =
CBA = 25°.
So,
=> CBD +
DCB = 180° (Angle sum Property.)
=> 90° +25° + DCB = 180°
=> 115° + DCB = 180°
=> DCB = 180° - 115°
=> DCB = 65°.
Now, in △ADC,
=> CD is the altitude to AB.
So,
=> ADC = 90°
=> CAD =
CAB = 65°.
So,
=> ADC +
CAD +
DCA = 180° (Angle sum Property.)
=> 90° + 65° + DCA = 180°
=> 155° +DCA = 180°
=> DCA = 180° - 155°
=> DCA = 25°
Hence, we get,