Use the appropriate formula to find the indicated figurate number.
-the 6th triangular number
A) $\mathrm { T } _ { 6 } = 18$
B) $\mathrm { T } _ { 6 } = 15$
C) $\mathrm { T } _ { 6 } = 42$
D) $\mathrm { T } _ { 6 } = 21$

Question

Quizplus · Accepted Answer

The formula for the nth triangular number is $ T_n = \frac{n(n+1)}{2} $. For the 6th triangular number, $ T_6 = \frac{6(6+1)}{2} = \frac{6 \times 7}{2} = 21 $.

Use the Appropriate Formula to Find the Indicated Figurate Number T6=18\mathrm { T } _ { 6 } = 18T6​=18

Use the Appropriate Formula to Find the Indicated Figurate Number $\mathrm { T } _ { 6 } = 18$