Question

find the value of 1-2+3-4+...+29-30​

Answer 1

This one is easy

Sum of n odd numbers is n²

So the sum 1+3+5...+29 is 225

And the sum of even numbers can be written as 2+4+6+8+.....+30

This can be written as 2(1+2+3+....+15)

Now we know that sum of first n natural numbers is n(n+1)/2

Applying it we get

2+4+8...+30=240

Evens are negative

So total sum becomes -15

So the answer is -15

Answer 2

Answer:

460

Step-by-step explanation:

Sum of all positive numbers= 240

The sum of all negative numbers= 225

240+225= 460