The general term formula of sequence {an} is an = 1n (n + 1) (n ∈ n *). If the sum of the first n terms is 1011, then the number of terms is______ ．

The general term formula of sequence {an} is an = 1n (n + 1) (n ∈ n *). If the sum of the first n terms is 1011, then the number of terms is______ ．

∵an＝1n(n+1)＝1n−1n+1∴Sn=a1+a2+… +an=1−12+12−13+… +1n − 1n + 1 = 1 − 1n + 1 = NN + 1 ｛ NN + 1 = 1011 ｛ n = 10, so the answer is: 10

The general term formula of sequence {an} is an = 1n (n + 1) (n ∈ n *). If the sum of the first n terms is 1011, then the number of terms is______ ．

∵an＝1n(n+1)＝1n−1n+1∴Sn=a1+a2+… +an=1−12+12−13+… +1n − 1n + 1 = 1 − 1n + 1 = NN + 1 ｛ NN + 1 = 1011 ｛ n = 10, so the answer is: 10

If we know the first n terms of an and Sn = a · 2N-1 + 16, then the value of a is ()
A. 13B. 12C. -13D. -12

∵ the sum of the first n terms of an is Sn = a · 2N-1 + 16, ∵ A1 = S1 = a + 16, A2 = s2-s1 = (2a + 16) - (a + 16) = a, A3 = s3-s2 = (4a + 16) - (2a + 16) = 2A, ∵ A2 = 2A (a + 16), the solution is a = - 13, or a = 0 (rounding)

Simple calculation 98 × 97-99 × 96

98x(96+1)-(98+1)x96=2

As shown in the figure, in the known isosceles trapezoid ABCD, ad ‖ BC, ad = BC = Ba, BD = BC, find the degree of ∠ a

Ad = BC = Ba, should be ad = DC = Ba?
AD‖BC,∠ADB=∠CBD,
AD=DC=BA,∠ADB=∠ABD,
So, CBD = abd, CBD = ABC / 2, CBD = ABC,
BD=BC,∠BDC=∠C,
Isosceles trapezoid ABCD, ab = DC, ∠ ABC = ∠ C, ∠ C = 2 ∠ CBD,
∠CBD+∠BDC+∠C=180°,
∠CBD+2∠CBD+2∠CBD=180°,
∠CBD=180°/5=36°,
∠A+∠ABD+∠ADB=180°,
∠A+∠CBD+∠CBD=180°,
∠A+36°+36°=180°,
∠A=180°-72°=108°.

Quarter o quarter o quarter o quarter o quarter = one eighth fill in the circle with the appropriate arithmetic symbol or bracket

1/4×1/4+1/4×1/4=1/8

A is a nonzero matrix of order n, the adjoint matrix of a is equal to the transpose of a, and it is proved that the determinant of a is not equal to 0

I have answered the same question

Little careless is doing an addition problem. He regards 9 in one digit of an addend as 6, and 3 in the tenth digit of another addend as 8. The sum of the results is 12. What's the correct answer?

If you add two numbers, and there are three in ten, even if you miscalculate, the result can't be 12

How to find the rank of matrix

The number of nonzero rows is the rank of the matrix

The solution of the equation: 1. 10 times of a number minus 25.5 equals 36. What's the number? 2. More than 5.6 times of a number
2. It's 5.6 times more than a number. The number of 4.2 is 8.4. What's the number? 3. A barrel of oil weighs 26.3kg. After half of it is poured out, the barrel weighs 14kg. How many kg are the oil and the barrel?

1:
10X-25.5=36 X=6.15
2:
5.6X+4.2=8.4 X=0.75
3:
Oil x barrel y
X+Y=26.3
X/2+Y=14
X=24.6
Y=1.7