Law of cosine:
c² = a² +b² -2ab*cosC.
Because the triangle is equilateral a=b=c=x,
and we can write,
x²=x² +x² -2xx*cosC
x² =2x² -2x²* cos C
-x² = -2x²*cos C
cos C= 1/2,
so m∠C=60⁰.
Because all sides are equal, and across of the equal sides should be equal angles, all angles will be also equal and = 60⁰.
2 to the 2nd power × 14 =Square root of 56
Answer:
a) 
b) t = 0.3 seconds
c) d = 4.9t²
d) d = 11 cm.
Step-by-step explanation:
One test involves catching a 1 m ruler and measuring the distance, d in meters, that the ruler will travel before being caught, the reaction time t in seconds is then calculated using the formula
.......... (1)
a) the simplified expression is
......... (2)
b) If d = 44 cm = 0.44 meters, from equation (2) we get,
t = 0.299 seconds ≈ 0.3 seconds (Approximate)
c) If we make d as the subject of the equation, then

⇒ d = 4.9t² .......... (3)
d) Now, if
seconds, then from equation (3) we get,
d = 4.9 (0.15)² = 0.11 meters = 11 cm (Answer)