In the baroque period (and even today) operas began with the it was an instrumental introduction to the opera. eventually, these were separated from the opera and led to the creation/birth of the orchestra.

In the baroque period (and even today) operas began with the overture. It was an instrumental introduction to the opera. Eventually, these were separated from the opera in Romantic era and led to the creation/birth of the orchestra  and orchestral music such as symphonic poems, whom composers such as Beethoven and Mendelssohn began to use the term to refer to independent, self-existing instrumental, programmatic works.

i think it was because of how protected egyptian civilization was was which allowed them to evolve without much outside influence.

simplify brackets

8 - 2a - 7 = a + 40

simplify 8 - 2a - 7 to -2a + 1

-2a + 1 = a + 40

add 2a to both sides

1 = a + 40 + 2a

simplify a + 40 + 2a to 3a + 40

1 = 3a + 40

subtract 40 from both sides

1 - 40 = 3a

simplify 1 - 40 o -39

-39 = 3a

divide both sides by 3

-39/3 = a

simplify 39/3 to 13

-13 = a

switch sides

a = -13