Come here for my friend Gabbie
Meeting ID: 987 5438 8675
Passcode: r7GTT8

Why whats happening ?

Since the numerical coefficient of the first term is only 1, we determine the number that needs to be added to both sides of the equation by squaring half of the second term. That is,
                                   third term = (15/2)² = 56.25
Thus, the missing terms are,
                          x² + 15x + 56.25 = 49 + 56.25
equal to,
                            x² + 15x + 56.25 = 105.25