The study of heat and heat changes is called
a. thermography
b. heat chemistry
c. thermal energy
d. thermochemistry

d. thermochemistry

Explanation:

Every substance has an amount of energy stored in its chemical bonds. In a chemical reaction, energy can be released or absorbed. Thermochemistry deals with the heat changes that take place in these reactions. That is, it is an application of thermodynamics to chemistry.

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west