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Cerrena [4.2K]
3 years ago
7

Find each product mentally. 7 times 3.8

Mathematics
1 answer:
lutik1710 [3]3 years ago
5 0
To do it mentally means to do it in your head

first do 7 * 3 = 21 in your head

than do 7 * 0.8 = 5.6 ( this might be hard to do in your head but you know 7*8 = 56 so add a decimal since it is 0.8 not 8 )

Add : 21 + 5.6 = 26.6

Final Answer : 26.6


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Answer:

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Step-by-step explanation:

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Since, terminal side of angle 'a' lies in quadrant 3, sine of angle 'a' will be negative.

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Similarly, terminal side of angle 'b' lies in quadrant 2, sine of angle 'b' will be  negative.

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cos(a + b) = (-\frac{1}{3})(-\frac{1}{4})-(-\frac{2\sqrt{2}}{3})(-\frac{\sqrt{15}}{4})

                = \frac{1}{12}-\frac{\sqrt{120}}{12}

                = \frac{1}{12}(1-\sqrt{120})

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Therefore, cos(a + b) = \frac{1}{12}(1-2\sqrt{30})

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