Express cosx + 3sinx in the form Rcos(x-a), where R > 0 and 0° < a < 90°, giving the exact value of R and the value of a correct to 2 decimal places.

Take the natural logarithm of both sides:

$$\ln y = \ln(Ae^{-kx^2})$$

Using logarithm properties $\ln(ab) = \ln a + \ln b$ and $\ln(e^p) = p$:

$$\ln y = \ln A + \ln(e^{-kx^2})$$ $$\ln y = \ln A - kx^2$$

This equation is in the form $Y = mX + C$, where $Y = \ln y$, $X = x^2$, the slope $m = -k$, and the y-intercept $C = \ln A$.

The given points are $(X_1, Y_1) = (0.64, 0.76)$ and $(X_2, Y_2) = (1.69, 0.32)$.

$$m = \frac{Y_2 - Y_1}{X_2 - X_1}$$ $$m = \frac{0.32 - 0.76}{1.69 - 0.64}$$ $$m = \frac{-0.44}{1.05}$$ $$m \approx -0.4190476$$

Since $m = -k$:

$$-k = \frac{-0.44}{1.05}$$ $$k = \frac{0.44}{1.05}$$ $$k \approx 0.4190476$$

Rounding to 2 decimal places, $k = \boxed{0.42}$.

Using the point-slope form $Y - Y_1 = m(X - X_1)$ or $C = Y_1 - mX_1$.
Using $(X_1, Y_1) = (0.64, 0.76)$ and $m = \frac{-0.44}{1.05}$:

$$C = 0.76 - \left(\frac{-0.44}{1.05}\right)(0.64)$$ $$C = 0.76 + \frac{0.44 \times 0.64}{1.05}$$ $$C = 0.76 + \frac{0.2816}{1.05}$$ $$C = 0.76 + 0.268190476...$$ $$C \approx 1.028190476$$

Since $C = \ln A$:

$$A = e^C$$ $$A = e^{1.028190476}$$ $$A \approx 2.79603$$

Rounding to 2 decimal places, $A = \boxed{2.80}$.