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lbvjy [14]
3 years ago
15

What is the sum of the first 4 terms of the arithmetic

Mathematics
1 answer:
liraira [26]3 years ago
8 0
a_6=8;\ a_{10}=13\\\\a_{10}-a_6=4r\\\\4r=13-8\\4r=5\ \ \ \ /:4\\r=1.25\\\\a_1=a_6-5r\\a_1=8-5\cdot1.25=8-6.25=1.75\\\\S_4=\frac{2a_1+(4-1)r}{2}\cdot4=(2a_1+3r)\cdot2=4a_1+6r\\\\S_4=4\cdot1.75+6\cdot1.25=7+7.5=14.5
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Step-by-step explanation:

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5 0
3 years ago
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6 0
3 years ago
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3 years ago
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