Q3. Which variable is NOT in the standard formula?
✔ Formula uses a, d, n or a, l, n. m is not used.
Show transcript
[Slide 1] Why Calculate Sum?
Imagine adding numbers from one to hundred. Doing it manually takes forever. We use a special formula for speed.
[Slide 2] The Sum Formula
This formula uses the count and pattern. You need the first term and common difference. Plug these values into the equation.
[Slide 3] Example Problem Setup
Let us find the sum of this sequence. We identify the starting number and gap. The count of terms is ten here.
[Slide 4] Solving the Example
Now substitute ten, two, and three inside. Simplify the bracket to get thirty one. Multiply five by thirty one for answer.
[Slide 5] Common Mistake Alert
Students often miss the minus one part. Sometimes they use the last term incorrectly. Always double check your substitution steps.
[Slide 6] Quick Recap
Remember there are two forms of formula. One uses last term instead of difference. Practice makes you perfect for exams.