Angle A Triangle 08A78A
1. **Problem statement:** Find angle $A$ in a triangle where side $b=28$, side $a=29$, and angle $C=52^\circ$. We can use the Law of Cosines or Law of Sines.
2. **Choosing the formula:** Since we know two sides and the included angle $C$, the Law of Cosines is appropriate:
$$c^2 = a^2 + b^2 - 2ab \cos C$$
But we don't know side $c$, so first find $c$:
$$c^2 = 29^2 + 28^2 - 2 \times 29 \times 28 \times \cos 52^\circ$$
3. **Calculate $c^2$:**
$$29^2 = 841$$
$$28^2 = 784$$
$$\cos 52^\circ \approx 0.6157$$
$$c^2 = 841 + 784 - 2 \times 29 \times 28 \times 0.6157$$
$$c^2 = 1625 - 2 \times 29 \times 28 \times 0.6157$$
Calculate the product:
$$2 \times 29 \times 28 = 1624$$
$$1624 \times 0.6157 \approx 1000.9$$
So,
$$c^2 = 1625 - 1000.9 = 624.1$$
4. **Find $c$:**
$$c = \sqrt{624.1} \approx 24.98$$
5. **Use Law of Sines to find angle $A$:**
$$\frac{a}{\sin A} = \frac{c}{\sin C}$$
Rearranged:
$$\sin A = \frac{a \sin C}{c}$$
Calculate:
$$\sin 52^\circ \approx 0.7880$$
$$\sin A = \frac{29 \times 0.7880}{24.98} \approx \frac{22.852}{24.98} = 0.9147$$
6. **Find angle $A$:**
$$A = \sin^{-1}(0.9147) \approx 66.4^\circ$$
**Final answer:** Angle $A$ is approximately $66.4^\circ$.