Finding the Third Proportional to 1,206 and 1,290

Step by Step Solution

1. Step 1: Write the proportion equation
   1,206 : 1,290 = 1,290 : x
2. Step 2: Convert to fraction form
   1,206/1,290 = 1,290/x
3. Step 3: Cross multiply
   1,206x = 1,290 × 1,290
4. Step 4: Simplify right side
   1,206x = 1,664,100
5. Step 5: Solve for x
   x = 1,664,100/1,206
6. Step 6: Final answer
   x = 1,379.85