Calculati urmatoarele sume 1+2++80. 2+4++100. 1+3+5++99. 3+7+11+15++43

(a)

1+2+3+..........+80

we can see that this is arithematic sequence

so, first term is

common difference is

total term is

now, we can find sum of nth term

now, we can plug values

and we get

...........Answer

(B)

2+4+6+.......+100

we can see that this is arithematic sequence

so, first term is

common difference is

total term is

now, we can find sum of nth term

now, we can plug values

and we get

..........Answer

(C)

1+3+5+...+99

we can see that this is arithematic sequence

so, first term is

common difference is

total term is

now, we can find sum of nth term

now, we can plug values

and we get

..........Answer

(D)

3+7+11+15+...+43

we can see that this is arithematic sequence

so, first term is

common difference is

total term is

now, we can find sum of nth term

now, we can plug values

and we get

..........Answer

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step-by-step explanation:

answer by yourhope:

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